Starting a DIY-mini-lathe

... as Sebastien pointed out, i'll show here the building of a mini-lathe-/CNC-lathe with alternative methods.

First the combination of a 4-jaws-chuck and a collet chuck mounting plate - i can change the chuck between an 1kW-servo-motor used as direct-drive lathe, or a 7Nm-microstepper atached to my CNC-mill as 'CNC-lathe'.

That looks really good. Do mention what kind of tooling method your going to employ. My first thought is, steppers for cnc lathing would make great contact free machining but couldn't hold up in a traditional lathe setup. Although thats depending on motors and materials.

... more than a year ago i made first tests with an extreme simple stepper-driven CNC-lathe-axis ... but had some problems with resonancy with my standard halfstep-drivers and the Nema34-200-steps-per-rev. stepper with 1.5Nm power, so stopped this and went on optimizing the CNC-mill ... atached are some images of my first stepper-lathe-axis and a roughing test.

Recently i've got some Precitec-steppers with drivers capable of 200 to 50000 steps per rev. and 7Nm torque, so i decided to make a second attempt with a 'realistic' setup

... and the last image is another sample of a small CNC-lathe-kombi ...

If I can get away with a smaller stepper on Big Bertha for the Z axis and use the two smaller 2.2NM steppers shown here for X and Y I will have a 3.5Nm stepper as a spare to try out on a lathe.. sort of in beteen the sizes you are using.

... i'll fill in the wiki when going further -- but this can take a wile, as i can only make progress some hours as weekends and at nights, if i'll avoid any noise ...

@Bodge It: - motors are strong enoug when over 1.5Nm, maybe even with 1Nm

The limiting range is the force of the mill-bit cutting in the material.

So when only using mill-bits smaller than 3mm diameter and avoiding fast rotation of the lathe-axis (best turn a step with the turning axis, then move the XZ-toolpath) you won't have much forces, even in hard materials ...

Another option would be to start with printed parts and bootstrap a stronger lathe. I'm just shamelessly repeating what cathal garvey just said in an email. My first thought on that is that with feedback you might not need a lot of stiffness to machine to tight tolerances.

... interesting question ... which stability is possible with plastic-chucks

The motors aren't reprappable yet, but all the holders and fixatures are - i remember a post or blog where someone made some lathe-supports out from sandfilled epoxy or plastic and embedded some berings for a steady rest (? - german "Lünette").

When fabbing moulds for metal-casting you can build your own chucks and tools, so it's not 100%-reprappability what's interesting, but more the methods and toolchains for DIY ...

Well, I jump on some parts here that have barely 20%
hexagonal infill and they will not break.
If they can build Car-parts from ABS the it should
be strong enough to hold some wood, plastic of
leightweight metal object centered.

Of cause even CNC-milled metal parts CAN in theory
be produced on a RepRap.
I just posted a Dremel milling-head for the RepMan
[www.thingiverse.com] yesterday.

> Best method should be laminating with carbon-fabric and heat the surface to fuse the fabric with the plastic beneath ... then fab the next slice, and so on ...

But then the strength would be very directional. Especially perpendicular to the layers, the strength is lacking, and this will not aid it's strength much in that direction.

I do think additive processes and composite materials hold a lot of promise.

I'm thinking of vertical arrangement of fibers or other materials. I wonder if we could push in short rods of hot metal, perhaps in pre-fabbed shafts, and then fill those up with plastic. Or extrude a metal thread with molten plastic around it. I've actually experimented with this and it seems to be feasible. You can pull out a thread of metal (< 0.1 mm) and when you extrude while doing this, some plastic is extruded around it. I'm not sure, but possibly you can couple the extrusion with a metal/fiber feed.

I think the fiber, even with some plastic will not have the specific heat to weld with the object unless that's locally heated as well and there's a channel for more (newly extruded) plastic to fit in. Alternatively, a thermoset material could be used around the fiber, requiring no heat to cure.

Even without fibers, this could increase speed AND add strength, since you could use a larger orifice printhead for filling vertical shafts that were left in the model for this purpose.

... update: - received the bigger stepper with 5:1-gearbox for the CNC-lathe ... have to order a collet for the 20mm-shaft first, then i can make a carrier with exchangeability for the stepper or servo.

The big stepper has the same parameters as the smaller, so i can use the same controller - it's only bigger, sturdier and with much more torque

... update: - got another motor with 4Nm without gearbox, so i can use the 2Nm-motor with 5:1-gearbox for a finer turning-table and the 4Nm-motor with 10000 steps per rev. as CNC-lathe-drive.

Atached an image with first fitting-test in the CNC-mill - when all fixing and counterparts are ready, i'll exchange the Y-axis with the lathe-axis and can mill complex 3D-parts with a turning axis ...

what you are trying to do is called "rotary table" ("rundschalttisch" in german)
some time ago i worked for "Fibro" in Germany, they produce such rotary tables
it is'nt quite easy to make them.. and they are pretty expensive
its driven by a worm drive, take a look at this picture and you will know what i mean:

i do'nt think you can do such a thing in home environment - some really difficult 5-axis milling is involved...
best thing you could do: picking up such a manual rotary table and attatch a stepper motor to it

... oh, it's not for me - I have different rotary tables, revolvers, advanced microtech or other 'serious hardware' stuff at hand.

The idea was to show other methodes, that possible are better DIY-able or can be made by 'rearranging' available equipment.

A surely DIY-able approach is a rotary head with two big diameter ring-bearings and printed outside-pulley as shown in the image attached below - but with printed parts instad of the (pricey) milled parts.

For most applications in the DIY-area you can get away with a NEMA-23 motor and belt-drive ...